The Once and Future King Book 1, Chapter 7
Arthur and Merlyn watch Kay practice jousting with a servant. Arthur tries to pretend he is not upset by the fact that Kay, because he is a "proper son," will be a knight, while Arthur, an adopted child, has to be Kay's squire. Merlyn sees that Arthur is upset: "'What is the matter now?' he enquired nastily. His inspection had shown him that his pupil was trying not to cry, and if he spoke in a kind voice he would break down and do it." Book 1, Chapter 7, pg. 56
Arthur tells Merlyn that he would not have a wife, but that he would have a "lady love"--he's young enough that he doesn't like girls, but he enjoys thinking of himself as a typical knight. Then Merlyn asks Arthur if he wants to see real knights jousting--something he has never seen before. Arthur says he wants to see King Pellinore joust, and Merlyn casts a spell.
At first Pellinore is afraid of Merlyn, because he is so solemn, but they quickly warm up to each other. Pellinore is challenged to a joust by Sir Grummore, even though they have never met and are friendly. In fact, the entire thing is scripted like a play---there are specific lines knights say that they remind each other of. It's not a graceful, legendary sight: the knights are crammed into hot, heavy armor, and they charge at each other clumsily. After a while they get irritated and begin to fight in earnest, but since it is very difficult to hurt someone hundreds of pounds of armor, they don't do much damage and eventually get tired. Sir Grummore conquers Pellinore, but then Pellinore cheats out of it. They chase each other around until they both get knocked unconscious. Merlyn assures Arthur that they are all right and will be best friends when they wake up, and casts the spell to return home.